Streptococcus thermophilus is a probiotic bacterium native to yogurt and other fermented dairy foods. It breaks down lactose, which can make dairy easier to digest. Many people take it in capsule or powder form to promote a healthy gut environment, often alongside other probiotic strains. Eating yogurt and kefir also supplies this bacterium directly.
Anyone with a weakened immune system or a serious medical condition should talk to a healthcare professional before adding a probiotic to their routine.